1. Field of the Invention
This invention relates to the field of compression and decompression of data.
2. Background Art
Computers are often used to process, play back, and display video data. This video data may come from sources such as storage devices, on-line services, VCRs, cable systems, broadcast television tuners, etc. Video data is memory intensive, that is, video data requires large amounts of memory for storage and use by a computer system. CD-ROMs provide one solution to the problem of storing large amounts of data. However, even the storage capabilities of a CD-ROM can be exceeded when storing motion picture length video data.
To reduce the transmission bandwidth and memory requirements when working with video data, various compression schemes have been developed so that less storage space is needed to store video information and a smaller bandwidth is needed to transmit it. Prior art video compression schemes include Motion JPEG, MPEG-1, MPEG-2, Indeo, Quicktime, True Motion-S, CinePak, etc.
A disadvantage of existing prior art compression schemes is their inability to provide adequate quality of playback in terms of format (spatial resolution), frame rate (temporal resolution) and color fidelity. In addition, the existing prior art schemes do not adequately compensate for the low data output rate of CD-ROMs. CD-ROMs suffer from a disadvantage of having a low data output rate compared to that needed for realistic video playback.
With respect to spatial resolution, many prior art schemes do not provide a "full screen" of video output. Here, full screen is defined as 640 by 480 color pixels. Many prior art compression schemes provide a small "box" that displays video data. Such small displays are difficult to view, and do not provide adequate playback of video data. Regarding temporal resolution, many of the prior art schemes provide "choppy" playback of video data, with jerky motion, and pauses in playback while new frame data is being generated.
Many source images include high resolution color information. For example, the source image may have a color resolution of 15, 24, or 32 bits per pixel. Many computer systems are only capable of providing 8 bit per pixel color output. This requires that the large number of colors of the source image be mapped to a smaller number of colors that can be displayed by the computer system. This step involves the use of a color look-up table (LUT). Prior art compression schemes typically rely on the host computer system to provide a color lookup table. These color lookup tables are not optimized for the particular source image, so unsatisfactory color display results.
Another disadvantage of prior art compression schemes is that they are "symmetrical". These schemes attempt to compress the data in the same time it takes to display the data. Typically, prior art compression schemes compress the data in a single pass, in real time or as close to it as possible. This limits the performance of prior art compression schemes.